channeling energy to harm undead and invisibility

[P=NP?]

if my cleric is invisible, as per the spell, and he channels positive energy to harm undead
is that considered an attack which would end the spell?

[HammerJack]

From page 305:

"Hostile Actions
Sometimes spell effects prevent a target from using hostile actions, or the spell ends if a creature uses any hostile actions. A hostile action is one that can harm or damage another creature, whether directly or indirectly, but not one that a creature is unaware could cause harm. For instance, lobbing a fireball into a crowd would be a hostile action, but opening a door and accidentally freeing a horrible monster would not be. The GM is the final arbitrator of what constitutes a hostile action."

So, do you know that there are undead and you're channeling to harm them? Then it's a hostile act.